TECHNICAL BULLETIN
Installation Options for Deck Lateral Load Connections
Background
When decks are supported by attachment to the primary structure, the International
Residential Code® (2000 through 2015 IRC) requires a positive attachment to that
building to resist lateral loads. These loads can result from wind or seismic forces
acting on a deck or from movements of the deck’s occupants. If the band joist,
deck ledger or deck joists were to pull away from the primary structure as a result
of lateral forces, the deck would not be supported for gravity (vertical) loads and
would likely collapse (see Figure 1).
To help builders achieve proper attachment, an approved method was added to
the 2009 IRC to resist lateral loads by using holdown devices with a minimum
allowable load of 1,500 pounds in at least two locations per deck. The 1,500-pound
holdowns connect a deck joist to a floor joist in the supporting structure that is
nailed to the floor sheathing above (see Figure 2). The 2015 IRC now includes a
second approved method that permits a holdown with an allowable load of 750
pounds in at least four locations per deck to fasten the deck joists to the top plate,
studs or headers within the supporting structure using a fully threaded ⅜" lag
screw (see Figure 3). This new option allows a positive attachment for the deck that
is ideal when the house joists are inaccessible.
Supporting
Structure
Band Joist
Floor
Sheathing
Deck Ledger
Lateral movement
of deck away from
supporting structure
Floor
Joist
Deck Joist
Collapse of
Unsupported
Deck
Figure 1
Floor Joist
2' Max.
from End
2' Max.
from End
Band Joist
Deck
Ledger
DTT2
Deck
Joist
(Ledger
screws
and joist
hangers not
shown for
clarity)
Figure 2 (1,500 lb. requirement)
Floor joists in supporting structure
(not shown) must be parallel to deck joists
Equal
Distances
2' Max.
from End
Supporting
Structure
2' Max.
from End
Top Plate
Deck
Ledger
DTT1Z
Deck
Joist
(Ledger
screws
and joist
hangers not
shown for
clarity)
The Simpson Strong-Tie® DTT1Z and
DTT2 deck tension ties have been
developed to provide versatile and
cost-effective solutions for these
critical connections. The DTT1Z is
supplied with a ZMAX® coating; the
DTT2 is available in ZMAX (DTT2Z) or
stainless steel (DTT2SS).
The DTT2 satisfies the 1,500-pound
requirement and is installed in pairs.
The DTT2 fastens to the wide face of
the deck and house joists with StrongDrive® SDS Heavy-Duty Connector
screws (included), and the pair is
anchored together with a ½" threaded
rod (washers included).
The DTT1Z satisfies the 750-pound
requirement and fastens to the narrow
or wide face of the deck joist with
Strong-Drive SD Connector screws or
nails and attaches to the supporting
structure with a fully threaded ⅜" lag
screw and washer (not included) or a
Strong-Drive SDWH Timber-Hex HDG
screw with an integral washer.
Figure 3 (750 lb. requirement)
©2015 Simpson Strong-Tie Company Inc. T-C-DECKLAT15 2/15 exp. 6/17
Installation Options for Deck Lateral Load Connections
Allowable Loads
Model
No.
DTT1Z
DTT2Z/DTT2SS
CL
¾"
13/16"
Anchor
Diam.
or Type
⅜"
or
SDWH5
½"
Allowable Tension Load (lbs.) (160)
Fasteners
Dry
11⁄2"
Wet
DF/SP
SPF/HF
DF/SP
SPF/HF
6-SD #9x1½"
840
840
840
755
6-10dx1½"
910
4
640
795
6404
8-10dx1½"
910
850
910
850
8-SDS ¼"x1½"
1825
1800
1825
1615
1.A llowable loads have been increased 60% for short-term loading with no further increase allowed.
2.Dry values are applicable to installations into wood with a moisture content that does not exceed 19%.
3.Wet values are applicable to installations into wood with a moisture content greater than 19% at time
of installation or in service. Values include an NDS wet service factor for the fasteners.
4.DTT1Z installations with allowable loads below 750 lbs. do not satisfy the 2015 IRC requirements for
deck-to-house lateral load connections.
5.DTT1Z installed with the Strong-Drive SDWH Timber-Hex HDG screw with a min. of 3" thread
penetration achieves the lesser of the table load or 855 lbs. SDWH installed with 3" of thread
penetration into dry lumber has an allowable withdrawal load (160) of 1380 lbs. into SP, 1225 lbs. into DF
and 1020 lbs. into SPF/HF.
6.Load values are valid if the product is flush with the end of the framing member or installed away
from the end.
7.FASTENERS: SD #9x11/2 (model SD9112) = 0.131" dia. x 11/2", 10dx11/2 = 0.148" dia. x 11/2" long.
71⁄8"
415⁄1
31⁄4"
"
6
1 7⁄1
615⁄1
"
6
"
6
DTT1Z
1 5⁄8
"
1 5⁄8
"
DTT2Z
Conditions Not Shown in the IRC
DTT1Z
10
10
10
10
10
10
3" Min.
Optional Side-Mount
Installation
3" Min.
DTT1Z
Do not over-drive
anchoring screw
Predrill 3⁄16" dia. hole for fully threaded
lag screw. Predrilling not required with
Strong-Drive® SDWH Timber-Hex HDG Screw.
(Siding not shown for clarity)
Figure 4
2
DTT1Z – 750-Pound Assembly
Condition 1 – Holdown Cannot Be Installed Flush
with Wall Sheathing
Unlike some holdowns, the DTT1Z seat is not
required to bear on sheathing or framing and can be
installed away from the wall to account for nonstructural siding, joist hanger interference or other
conditions. Longer screw anchors may be required
to ensure a minimum of 3" thread penetration by a
fully threaded lag screw or Strong-Drive® SDWH
Timber-Hex HDG screw into the wall framing.
Condition 2 – Top of Wall Plate Does Not Align
with Bottom of Deck Joist
The 2015 IRC detail shows a holdown installed on
the bottom of the joist. However, the DTT1Z was
tested and developed using 1½" fasteners into
either the narrow edge or wide face of a 2x member,
allowing the DTT1Z to be installed at any location
along the depth of the joist.
©2015 Simpson Strong-Tie Company Inc. T-C-DECKLAT15
The IRC details describe particular methods that are appoved and do not represent all common framing conditions. When
these are encountered, alternate methods of construction may need to be approved by the building official to ensure they
satisfy the intent of the code and are at least equivalent to the prescribed method. Several alternate construction methods
are shown here.
Installation Options for Deck Lateral Load Connections
24"
(house wall framing
not shown)
DTT1Z – 750-Pound Assembly (cont.)
8½" Typ. Spacing
3"
1½"
1" Typ.
W S 22
W S 22
W S 22
3
3
3
W S 22
W S 22
W S 22
3
3
Joist
Extension
(3¾" Max.)
3
27XX
1½"
(Siding not
shown for clarity)
¾" to Centerline
of DTT1Z Anchor
6-Strong-Drive® SDWS TIMBER
Screws (Model No. SDWS23000DB)
Figure 5A
(side view)
2x8x24" Blocking for Extensions up to 1¾"
2x10x24" Blocking for Extensions up to 3¾"
Figure 5B
(end view)
(Siding
not shown
for clarity)
4¼"
1½"
Deck Ledger
27XX
DTT1Z
2-Strong-Drive® SDWS TIMBER
Screws (Model No. SDWS22400DB)
into each joist
Extend
4" Min.
Each Side
Figure 6A
(side view)
2x8 Blocking
Center DTT1Z on Wall Stud
(wall sheathing not shown for clarity)
Figure 6B
(end view)
Condition 3 – Wall Plate Is
Below Bottom of Deck Joist
The DTT1Z has been tested
with the blocking assembly
shown in Figures 5A and 5B,
which allows the holdown to
be lowered up to 3¾" below
the bottom of the deck joist
in order to anchor into the
center of a wall plate.
Condition 4 – Wall Stud Receiving
Anchor Does Not Align with Deck Joist
The DTT1Z may be positioned on
horizontal 2x8 blocking that can be
installed between two deck joists, as
shown in Figures 6A and 6B. This
allows the holdown to be centered on a
wall stud that does not align with a deck
joist. Alternatively, an additional deck
joist can be added to the deck to align
with a wall stud (not shown).
(House wall(House
framing
wall framing
not shown)not shown)
DTT1Z
1015
1015
1015
DTT1Z
1015
1015
1015
W S 22
W S 22
1015
W S 22
©2015 Simpson Strong-Tie Company Inc. T-C-DECKLAT15
3
2"
1015
W S 22
3
1015
W S 22
3
1015
3
W S 22
3
1015
W S 22
3
1015
1"
1"
27XX
1"
27XX
1"
3
W S 22
3
2"
12"
12"
3½" Typ. 3½" Typ.
®
®
4-Strong-Drive
4-Strong-Drive
SDWS TIMBER
SDWS TIMBER
Screws (Model
Screws
No.(Model
SDWS22300DB)
No. SDWS22300DB)
(Siding not(Siding not
shown for clarity)
shown for clarity)
2x4x12" Blocking
2x4x12" Blocking
Figure 7A
(side view)
Figure 7B
(end view)
Condition 5 – Joist Hanger Flanges
Interfere with Screw Anchor
In some cases it may be necessary to
position the DTT1Z in a location that
conflicts with a joist hanger or other
obstruction. Figures 7A and 7B detail an
assembly that allows the DTT1Z to be
installed 1½" away from the face of the
deck joist.
2⅝" Min. Anchor
Embedment
3¾" Min. to
top of concrete
1015
1015
1015
⅜"x7" Mechanically Galvanized
Wedge-All® Anchor
(Model WA37700MG)
1015
1015
1015
Condition 6 – Ledger Attaches to Concrete Foundation Wall
As an alternative to using a Strong-Drive® SDWH Timber-Hex HDG
screw or fully threaded ⅜" lag screw, the DTT1Z may be anchored with
a ⅜" mechanically galvanized Wedge-All® anchor (as shown in Figure 8)
to achieve the 750-pound load requirement.
Figure 8
Condition 7 – Floor Joist Framing Is Perpendicular to the Deck Joist (Not Shown)
The IRC states that the 750-pound holdown detail is “applicable where the floor joists are parallel to deck joists.”
For floor joists perpendicular to deck joists, refer to Condition 2 for the DTT2 – 1,500-Pound Assembly on the next page.
3
Installation Options for Deck Lateral Load Connections
DTT2 – 1,500-Pound Assembly
Condition 1 – Floor Joist Framing Does Not
Line Up with the Deck Joist (Figure 9)
The DTT2 may be installed with a maximum allowable offset of 1½"
when the ties are installed at least 18" apart (see Figure 9). Larger
offsets may require an additional deck joist be added to line up with
the floor joist.
DTT2
Floor
Joist
1½" Max.
Offset
Full-height blocking between joists is a common construction
method when lateral load is applied perpendicular to floor framing.
The blocking for this application would have to extend into the
floor framing far enough to permit enough fasteners from the floor
sheathing to transfer 1,500 pounds. An 8d common nail (0.131" x
2½") through 23⁄32" wood structural-panel floor sheathing (G = 0.50)
into SPF or better blocking (G ≥ 0.42) has an allowable lateral design
value of 131 pounds (1.60 load duration factor*). This installation
would require 12 nails through the floor sheathing into the blocking.
It is recommended that the blocking extend into the floor at least two
joist bays and the DTT2 be installed in the farthest blocked bay
(see Figure 10). When nails into the floor sheathing cannot
be installed, see Condition 5 below.
½" Dia.
Threaded Rod
Floor
Sheathing
Nailing
Band Joist
Band Joist
Deck Ledger
Deck Ledger
Deck Joist
DTT2
DTT2
Deck Joist
Figure 9
*A load duration factor of 1.60 corresponds to a 10-minute
duration of maximum load; adjust for other durations. Figure 10
Fasteners between deck ledger and
supporting structure are not shown for clarity
Condition 3 – Floor Joist is a
Wood Truss or I-Joist
The DTT2 must be installed on a minimum 2x
wood member. Some wood truss and I-joist
manufacturers have developed details to attach
a horizontal 2x member to their product to
transfer a 1,500-pound lateral load. Contact the
manufacturer of the engineered floor component
for more information.
½" Dia.
Threaded Rod
18" Min.
for Offset
Condition
Condition 2 – Floor Joist Framing Is
Perpendicular to the Deck Joist (Figure 10)
Floor Joists
DTT2
Full-Height
Blocking
½" Dia.
Threaded Rod
DTT2
Vertical
Overlap
(4" Min.)
Condition 4 – Top of Deck Steps Down
Below Top of Floor (Figure 11 and 12)
Figure 11
½" Dia. Anchor
(Refer to Anchoring and
Fastening Systems for
Concrete and Masonry
catalog for post-installed
anchor products)
DTT2
Figure 12
The DTT2 may be installed with as little as 4" of
vertical overlap between the floor joist and deck
joist depths. Note that the code-prescribed connection between the deck ledger and band joist to support gravity
loads will require much more overlap. When a step down results in a deck ledger that is attached to a concrete
or grout-filled CMU foundation wall, the DTT2 may attach to a ½" diameter anchor rod that is attached to the wall
(ledgers are not permitted to be supported by stone or masonry veneer). The anchorage and the wall should be
designed to support a 1,500-pound lateral load (see Figures 11 and 12).
Condition 5 – No Access to the Top of the Floor Sheathing (Figure 13)
When the floor sheathing-to-joist nailing specified in the IRC cannot be installed, an alternate connection
capable of transferring 1,500 pounds to the floor sheathing is required. Simpson Strong-Tie has evaluated
the A35 framing angle installed in ½" minimum plywood or OSB sheathing with SPAX® #6 x ½" pan-head,
full-thread screws.* The installation shown in Figure 13 has an allowable lateral load of 425 pounds per
A35 (based on a 3.0 factor of safety). Use four A35 framing angles to meet the 1,500-pound requirement.
When fastened to full-height blocking (see Condition 2), use at least two A35 framing angles on each block.
*Available from Simpson Strong-Tie® in 200-count boxes, Model Number SPAX#6x1/2-R200
Condition 6 – No Access to Floor Joist
Latera
l Load
SPAX Screws*
into Subfloor
8dx11⁄ 2" Nails
into Floor Joist
or Blocking
Figure 13
When there is no access to the floor joists in the primary structure, the DTT1Z 750-pound assembly
(as shown in this technical bulletin) offers an easy-to-install solution. Where a positive connection to the
primary structure cannot be made or verified during inspection, the IRC requires the deck to be self-supporting.
This technical bulletin is effective until June 30, 2017, and reflects information available as of February 1, 2015.
This information is updated periodically and should not be relied upon after June 30, 2017; contact Simpson Strong-Tie
for current information and limited warranty or see www.strongtie.com.
©2015 Simpson Strong-Tie Company Inc. • P.O. Box 10789, Pleasanton, CA 94588
T-C-DECKLAT15 2/15 exp. 6/17
800-999-5099
www.strongtie.com